@Terry Because of Toufiq not understanding the problem, I have checked the helix3.php.
To resolve the issue, you need to change the following line.
/plugins/system/helix3/helix3.php Line: 60
before:
if( !JFactory::getApplication()->isClient('administrator') ) {
after:
if( !JFactory::getApplication()->isClient('api') && !JFactory::getApplication()->isClient('administrator') ) {
This makes sure the code is not called, if a api-request was made and prevents the error.
The root cause is, when a api call is made, there is no template-instance for the menus and this leads to this error.
Please be also aware, that Joomshaper does not activly support helix3 anymore. "EOL = end of life"
-> https://github.com/JoomShaper/Helix3
I will add this fix to my pullrequest and hope they will fix it asap.
Have a nice week.
addendum: Please note that when updating the Melvin template, this change will also be lost and the problem can or will occur again.