Application Cross-Scope privilege
Designer is a scoped application and requires read access to tables (including custom tables) to receive data from. The commit function requires create access to tables.
To grant read / create cross-scope access to tables please follow the following instruction, which can be performed by ServiceNow System Administrators:

A – Please ensure that Designer is selected as the Source Scope.
B – Select the Target Scope which needs to reflect the scope, where the tables are belonging to e.g. UPMX for ins·pi’s UPM·X application.
C – Enter the table name here e.g. x_inpgh_upmx_value_chain.
D – Select Read, if you want your Designer users only to read data from the tables. Select Create, to allow x_inpgh_des.commit role users to create elements in the target table.
E – Select Allow to provide access to the target table.