Value cannot be changed for Project Code

Im changing the project type from internal to external and non-billable to time & material under the Project Billing Type then having this issue Value cannot be changed for Project Code any suggestions

Can you share the Screenshot of issue

Project Code is your custom created field?

yes

Can you show m what is in the Options

PROJ-.####
PROJ-.{customer_name_naming}.-.####

This serial number contain value of this field customer_name_naming

After save the project, if you change the value of this field customer_name_naming then error will come. that’s is correct.

Project Code is the ID of record. After save the record, you can’t change the ID

so in this case I cant change the project type from internal to external

If the fieldname of Project Type field is customer_name_naming then you can’t change it