Update MSSQL table method:

1) Run the following query in AtomiaBilling database:

use AtomiaBilling
select * from plugin_configuration
where value like '%BIL-IF%'

2) The output of this query should return one row. Remember it's id cell value, since it is going to be used to update the table, and then copy the value cell content to your text editor of choice, since it contains some json code that needs to be altered. Precisely, last two lines need to be removed:

{
"DnsCategoryName": "DNS",
"DomainRegistrationCategoryName": "Domain",
"DomainTransferCategoryName": "DomainTransfer",
"HostingCategoryName": "Hosting",
"OnlinePaymentUrl": "https://billing.dev.atomia.com/Invoice/{0}/{1}/OnlinePayment",
"OwnDomainArticleNumber": "XSV-OD",
"RegisteredDomainsLimit": 0,
"ResetPasswordUrl": "https://hcp.dev.atomia.com/ResetPasswords/{0}/{1}",
"SendInvoiceByPostItem": "BIL-IF",
"SetupFeeItem": "BIL-SF"
}

3) Update the MSSQL table with the following query, and commit afterwards if everything runs OK. Remember to alter the id string from the "where" condition with your actual id value that you got from the previous SQL query:

begin tran
update plugin_configuration set value = ('{         "DnsCategoryName":"DNS",         "DomainRegistrationCategoryName":"Domain",         "DomainTransferCategoryName":"DomainTransfer",         "HostingCategoryName":"Hosting",         "OnlinePaymentUrl":"https://billing.dev.atomia.com/Invoice/{0}/{1}/OnlinePayment",         "OwnDomainArticleNumber":"XSV-OD",         "RegisteredDomainsLimit":0,         "ResetPasswordUrl":"https://hcp.dev.atomia.com/ResetPasswords/{0}/{1}"  }') where id = '01748D36-E294-42A0-8AC0-BAF1279C93D5'

4) Restart the IIS with the "iisreset" command from the Command Prompt or Powershell with an administrative priviledges.

5) Clear your browsers cache and cookies before testing.

6) Voilà! The invoice fee is disabled! :)