Sendgrid Plugin by Copilot

Hello @copilot ,
I am having trouble similar to the original post, but my error is slightly different:

Plugin action Send multiple basic emails (sendgrid) error:
TypeError: Cannot read property ‘slice’ of null
at eval (eval at build_function (/var/task/util/util_harness.js:34:12), :48:15)
at eval (eval at build_function (/var/task/util/util_harness.js:34:12), :332:8)
at /var/task/plugin_api_v3.js:250:27
at run_fn (/var/task/u.js:550:18)

I understand it’s a data error, but I am not sure where I am messing up! please help