Checkbox does not integrate with ACF user field checkbox

I have a 4 field checkbox on a user registration form

When 1 field is selected, it gets passed to the user fields ok with a database string of

a:3:{s:4:”name”;s:16:”Interests Choice”;s:4:”type”;s:5:”radio”;s:5:”label”;s:7:”Shiurim”;}

When 2 or more fields are selected it fails to pass the correct code

It sets the database to

a:3:{s:4:”name”;s:9:”Interests”;s:4:”type”;s:8:”checkbox”;s:5:”label”;a:2:{i:0;s:10:”Networking”;i:1;s:7:”Shiurim”;}}

It should set the database to

a:2:{i:0;s:10:”Networking”;i:1;s:7:”Shiurim”;}

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