Updating Post Meta using Pro Forms

I’m trying to update the post meta of a CPT post of mine.

I want to check a checkbox after submit (meta box).
I believe this is done with value 1 (checked checkbox is 1 in metabox docs).
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However, i’ve tried everything in the ‘Post Meta Name’ field. But it never seems to update.

The field is in a group, and whenever i take it out of this group it will update, but I cannot seem to update the field when it’s in a group.

I’m using the Custom Tables extension from meta box. But this didn’t seem to matter since when I take the field out of a group it is able to update…

Any help is greatly appreciated, i cannot seem to figure it out…

(ps, the ‘reparatie werkzaamheden’ group is a clonable group.)