Steps to reproduce:

1. Create a template for monitoring web services on multiple servers
2. Create LLD with macros {#INTNAME} and {#URL}
3. Create Item prototype with type HTTP Agent
4. Type {#INTNAME} in Key 

Result:

Zabbix not save item prototype due to error:

• Invalid key "{#INTNAME}" for item prototype "Service {#INTNAME}" on "Template Internal Services Availability": incorrect syntax near "{#INTNAME}".

See screenshot 1

Because of this, it is impossible to create a prototype item.

If enter any value in the key without a macro, save the element prototype and apply the template to the server, an error appears when creating elements with a duplicate key.

See screenshot 2