Error 500 - Add a participants

When I create a conversation and then try to invite someone I will get a error 500 (if you do not reload the page)

send @ site-2.1.7.min.js:156
v.send @ site-2.1.7.min.js:150
ajax @ site-2.1.7.min.js:150
ajax @ conversekit-1.1.2.min.js:3
{insertParticipant} click @ conversekit-1.1.2.min.js:21
(anonymous) @ site-2.1.7.min.js:311
dispatch @ site-2.1.7.min.js:89
r.handle @ site-2.1.7.min.js:85

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