Hi Shanushika,
It sounds like you're building a tool that returns content items via the deep linking content selection flow. Normally, the custom property of the linkitem (https://www.imsglobal.org/lti/model/mediatype/application/vnd/ims/lti/v1/contentitems%2Bjson/index.html#LtiLinkItem) is what's used to return arbitrary data alongside a content item (e.g. guid of the item), for use in the subsequent launch of said item later on, via a generic launch URL (tool/launch.php). Then, during launch, the custom claim (http://www.imsglobal.org/spec/lti/v1p3/#custom-properties-and-variable-substitution) is used to send this information over to the tool. Effectively you're using a claim to send this data back and forth, rather than via URL params.
Does this answer your question?
Jake
It sounds like you're building a tool that returns content items via the deep linking content selection flow. Normally, the custom property of the linkitem (https://www.imsglobal.org/lti/model/mediatype/application/vnd/ims/lti/v1/contentitems%2Bjson/index.html#LtiLinkItem) is what's used to return arbitrary data alongside a content item (e.g. guid of the item), for use in the subsequent launch of said item later on, via a generic launch URL (tool/launch.php). Then, during launch, the custom claim (http://www.imsglobal.org/spec/lti/v1p3/#custom-properties-and-variable-substitution) is used to send this information over to the tool. Effectively you're using a claim to send this data back and forth, rather than via URL params.
Does this answer your question?
Jake