Hi kongen.1
I am not sure if I can answer this 100% accurately, and I do not want to give you false information, that said....
1 FieldX and GroupX
FieldX is for repeating ONE field... It looks like you are just repeating the Media field... so use FieldX, NOT GroupX.
GroupX is for a collection of fields ie 'title', 'image', 'description'. You see on the GroupX config window the option to select a content type, generally, you make a content type of fields that you want grouped, then display the content type using GroupX.
2 Custom | Article | db_column_machine_name[field_in_form_machine_name]
The above format should be used for your form. See the image at bottom of page.
In the image I have it as:
Format / Object: Custom | Article | my_column[field_to_repeat]
In the config for the fieldX field, it requests the field. This is the field you want to repeat ie your media field... in the image it is
field_to_repeat
You can store like this:
Custom | Article |field_to_repeat
But then you loose the ability to call a value individually ie if you have 3 images stored, you can't call the 2nd image or just the 3rd.
When I find the example I will post it here...
3 Resources
seblod-2-x-field-x - helpful to a degree, not sure it is 100% accurate, might have been then ie it does not have to be limited to storing in introtext column.
how-to-use-plugin-field-fieldx - confuses me each time I read it, but there is info in there that can be helpful.
how-to-manage-fields-storage - probably the best of the bunch
Good luck
Hope I have helped rather than hindered.