Problem: Connecting Two CPT's with intermediary CPT via CRED New Form
Solution: You can use CRED hook "cred_save_data" to do any customization you need and to connect the post using intermediary post entry.
You can find proposed solution, in this case, with the following reply: https://toolset.com/forums/topic/connecting-two-cpts-with-intermediary-cpt-via-cred-new-form/#post-871487
Relevant Documentation: https://toolset.com/documentation/programmer-reference/cred-api/#cred_form_validate
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