3826635 - Why am I not able to add a User Supplied Hotel to the existing Car only booking in Concur Travel?

Traveler is trying to add a User Supplied Hotel to Car only booking, but they are receiving an error and are unable to complete the request. When they try to add this in Sabre GDS no error is returned.

GDS-Hotel-Internal error unable to complete when trying to add user supplied hotel to existing car reservation. Able to add directly in GDS-Sabre , KBA , CON-CA-TLS-IEM-IMP , Import Credit Cards , CON-CA-ADM , Administration , CON-MOB-TRV-HTL , Hotel , Problem