To enable the subscription service to be inserted several times on the same page, the submission form must contain a hidden field with the zone item ID.
If you have overloaded the graphic rendering of the subscription form, add the following element:
<input type="hidden" name="zoneitem-id" value="{ametys:zoneItemId()}"/>
<input type="hidden" name="zoneitem-id" value="{ametys:zoneItemId()}"/>
<input type="hidden" name="zoneitem-id" value="{ametys:zoneItemId()}"/>
Your form contains other hidden fields (category, page-id). Look for these fields in your overloads and add the "zoneitem-id" field in the same place if you find them.