Profile: tims-9

Problem:

Setup Repeating Fields sort order using PHP codes.

Solution:

Toolset Types plugin is using a custom field to store the sort order of Repeating Fields, the field slug is "_wpcf-{field-slug}-sort-order", and field value is in serialized array format.

For example Repeating Fields "start-date", the sort order field slug is "_wpcf-start-date-sort-order", and field value is:

Above numbers 648, 649 and 650 are "meta_id" values of each instance, you can get them with add_post_meta() function of your PHP codes, see WP document:
https://developer.wordpress.org/reference/functions/add_post_meta/#return
Return #Return
(int|false) Meta ID on success, false on failure.

Then update the sort order field value with function update_post_meta().

Then update the sort order field value with function update_post_meta().

Relevant Documentation:

https://developer.wordpress.org/reference/functions/add_post_meta/#return

https://developer.wordpress.org/reference/functions/update_post_meta/