Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires php ^8.1 but your php version (8.0.30) does not satisfy that requirement.

Process completed with exit code 2.

src/SAML2/Assertion/Transformer/NameIdDecryptionTransformer.php:103:25: InvalidArgument: Argument 1 of SimpleSAML\SAML2\XML\saml\Subject::__construct expects SimpleSAML\SAML2\XML\saml\IdentifierInterface|null, but SimpleSAML\XML\ElementInterface provided (see https://psalm.dev/004)

src/SAML2/Certificate/Key.php:18:22: MissingTemplateParam: SimpleSAML\SAML2\Certificate\Key has missing template params when extending ArrayAccess, expecting 2 (see https://psalm.dev/182)

src/SAML2/Configuration/CertificateProvider.php:19:16: MismatchingDocblockReturnType: Docblock has incorrect return type 'iterable<array-key|mixed, mixed>|null', should be 'Traversable|array<array-key, mixed>|null' (see https://psalm.dev/142)

src/SAML2/Configuration/IdentityProvider.php:21:16: MismatchingDocblockReturnType: Docblock has incorrect return type 'iterable<array-key|mixed, mixed>|null', should be 'Traversable|array<array-key, mixed>|null' (see https://psalm.dev/142)

src/SAML2/Configuration/PrivateKey.php:54:16: RedundantCondition: string can never contain null (see https://psalm.dev/122)

src/SAML2/Configuration/ServiceProvider.php:22:16: MismatchingDocblockReturnType: Docblock has incorrect return type 'iterable<array-key|mixed, mixed>|null', should be 'Traversable|array<array-key, mixed>|null' (see https://psalm.dev/142)

src/SAML2/HTTPArtifact.php:95:16: UndefinedClass: Class, interface or enum named SimpleSAML\Utils\HTTP does not exist (see https://psalm.dev/019)

src/SAML2/HTTPArtifact.php:168:30: UndefinedClass: Class, interface or enum named SimpleSAML\Configuration does not exist (see https://psalm.dev/019)

src/SAML2/HTTPArtifact.php:171:54: NullArgument: Argument 2 of SimpleSAML\SAML2\XML\samlp\ArtifactResolve::__construct cannot be null, null value provided to parameter with type DateTimeImmutable (see https://psalm.dev/057)

src/SAML2/HTTPArtifact.php:194:24: UndefinedMethod: Method SimpleSAML\SAML2\XML\samlp\AbstractMessage::addValidator does not exist (see https://psalm.dev/022)

tests/SAML2/XML/mdui/DiscoHintsTest.php:153:73: UndefinedInterfaceMethod: Method SimpleSAML\XML\ElementInterface::getXML does not exist (see https://psalm.dev/181)

Process completed with exit code 2.

Process completed with exit code 1.

src/SAML2/Binding.php:102:53: PossiblyInvalidArgument: Argument 2 of array_key_exists expects array<array-key, mixed>, but possibly different type array<array-key, mixed>|null|object provided (see https://psalm.dev/092)

src/SAML2/Binding.php:102:97: PossiblyInvalidArgument: Argument 2 of array_key_exists expects array<array-key, mixed>, but possibly different type array<array-key, mixed>|null|object provided (see https://psalm.dev/092)

src/SAML2/Binding.php:104:55: PossiblyInvalidArgument: Argument 2 of array_key_exists expects array<array-key, mixed>, but possibly different type array<array-key, mixed>|null|object provided (see https://psalm.dev/092)

src/SAML2/HTTPPost.php:53:33: PossiblyNullArgument: Argument 1 of base64_encode cannot be null, possibly null value provided (see https://psalm.dev/078)

src/SAML2/HTTPPost.php:85:45: PossiblyInvalidArgument: Argument 2 of array_key_exists expects array<array-key, mixed>, but possibly different type array<array-key, mixed>|null|object provided (see https://psalm.dev/092)

src/SAML2/HTTPPost.php:87:52: PossiblyInvalidArgument: Argument 2 of array_key_exists expects array<array-key, mixed>, but possibly different type array<array-key, mixed>|null|object provided (see https://psalm.dev/092)

src/SAML2/HTTPPost.php:94:50: ArgumentTypeCoercion: Argument 1 of SimpleSAML\XML\DOMDocumentFactory::fromString expects non-empty-string, but parent type string provided (see https://psalm.dev/193)

src/SAML2/HTTPPost.php:96:52: ArgumentTypeCoercion: Argument 1 of SimpleSAML\XML\DOMDocumentFactory::fromString expects non-empty-string, but parent type false|string provided (see https://psalm.dev/193)

src/SAML2/HTTPPost.php:112:44: PossiblyInvalidArgument: Argument 2 of array_key_exists expects array<array-key, mixed>, but possibly different type array<array-key, mixed>|null|object provided (see https://psalm.dev/092)

src/SAML2/HTTPRedirect.php:65:29: PossiblyNullArgument: Argument 1 of gzdeflate cannot be null, possibly null value provided (see https://psalm.dev/078)

tests/SAML2/XML/md/EntityDescriptorTest.php:277:75: PossiblyNullReference: Cannot call method format on possibly null value (see https://psalm.dev/083)

tests/SAML2/XML/md/EntityDescriptorTest.php:394:89: PossiblyNullReference: Cannot call method format on possibly null value (see https://psalm.dev/083)

tests/SAML2/XML/md/RoleDescriptorTest.php:190:83: PossiblyNullReference: Cannot call method format on possibly null value (see https://psalm.dev/083)

tests/SAML2/XML/md/RoleDescriptorTest.php:238:83: PossiblyNullReference: Cannot call method format on possibly null value (see https://psalm.dev/083)

tests/SAML2/XML/md/RoleDescriptorTest.php:256:54: PossiblyNullReference: Cannot call method saveXML on possibly null value (see https://psalm.dev/083)

tests/SAML2/XML/saml/AssertionTest.php:322:80: ArgumentTypeCoercion: Argument 1 of SimpleSAML\XML\DOMDocumentFactory::fromString expects non-empty-string, but parent type false|null|string provided (see https://psalm.dev/193)

tests/SAML2/XML/saml/AssertionTest.php:322:80: PossiblyNullArgument: Argument 1 of SimpleSAML\XML\DOMDocumentFactory::fromString cannot be null, possibly null value provided (see https://psalm.dev/078)

tests/SAML2/XML/saml/AssertionTest.php:336:96: PossiblyNullReference: Cannot call method format on possibly null value (see https://psalm.dev/083)

tests/SAML2/XML/saml/AssertionTest.php:576:16: DocblockTypeContradiction: Cannot resolve types for $mValue - docblock-defined type array<array-key, SimpleSAML\SAML2\XML\saml\AttributeValue|SimpleSAML\SAML2\XML\saml\IdentifierInterface> does not contain SimpleSAML\SAML2\XML\saml\NameID (see https://psalm.dev/155)