403 error when updating form info

hi there
we have a hosted service with the following
install environment:
MySQL – 5.6.43
PHP – 7.2
WP – 5.1.1
nuBuilder plugin – 1.5

i have installed the nuBuilder plugin in WP via the plugin manager within WP.
i am now following your Pizzeria how to guide.
i am able to create the initial forms (customer, menu , sizeprice etc) using the fast forms button on the builders tab.
i can see the forms that i created when i click of the ‘forms’ button in the setup tab.
when i try and rename the description and code in the setup/forms section ie:
table: customer
code: FF0 > CUS (as per you pizzaria guide) and then click the red save button i get a 403 Forbidden error.

if i open myPHPAdmin, i can see the tables have been created in the sql DB (table – customer, menu etc) so it seems that WP/nubuilder is talking to mysql.

any idea on what would be causing this?

many thanks in advance.
ryan king