It seems most things related to plug-in's are related to the SuiteScript Permission.

I've added the SuiteScript: Full Permission to the Custom Role but still get an error when trying to access the page.

Other candidates are • Lists - Companies: Allows usage of the Modified By field in Custom GL Lines Plug-in Revisions search. • Lists - Custom GL Lines Plug-in Audit Log: Allows usage of the Custom GL Lines Plug-in Audit Log search. • Lists - Custom GL Lines Plug-in Audit Log: Allows usage of the Custom GL Lines Plug-in Revisions search. • Lists - Custom GL Lines Plug-in Audit Log: Allows usage of the Search Custom GL Lines Plug-in Audit Log task. • Setup - Financial Institution Records: Allows viewing and editing of the Bank Statement Parser Plug-in record. • Setup - Review Custom GL Plug-in Executions: Allows usage of the Review Custom GL Plug-in Executions task. • Setup - Review Custom GL Plug-in Executions: Allows viewing and editing of the Review Custom GL Plug-in Executions record. • Setup - SuiteScript: Allows usage of the Custom Plug-in Types task. • Setup - SuiteScript: Allows usage of the Manage Plug-ins task. • Setup - SuiteScript: Allows usage of the New Custom Plug-in Type task. • Setup - SuiteScript: Allows usage of the New Plug-in task. • Setup - SuiteScript: Allows usage of the Plug-in Implementations task. • Setup - SuiteScript: Allows viewing and editing of the Custom Plug-in Implementation record. • Setup - SuiteScript: Allows viewing and editing of the Custom Plug-in Type record. • Setup - SuiteScript: Allows viewing and editing of the Plug-in record.