Cannot convert value of type Text to type Number issue

[Anonymous]

I'm trying to make a column which holds an IF statement for the text in another column. However I get the following error and I don't know why. There are no numbers at all in the original column and the new column is also formatted as text, so unsure why its trying to change it to number?

[Tahreem24]

Could you please share the screen shot of the error and sample input and expected output?

[Anonymous]

I'm trying to attach pictures but I only have the option to use the image source rather than upload an image from my PC so I'm struggling with that aspect.

The IF statement is: 

Call Type Definition = if('Phone Data'[Call Type]="conf_in","Phone Bridge In",if('Phone Data'[Call Type]="conf_out","Phone Bridge Out",if('Phone Data'[Call Type]="pstn_in","Calls In",if('Phone Data'[Call Type]-"pstn_out","Calls Out",if('Phone Data'[Call Type]="pstn_out_forwarding","Forwarded Call", if('Phone Data'[Call Type]="pstn_out_transfer","Transfered Call",'Phone Data'[Call Type]))))))

The error is:

Cannot convert value 'pstn_out_forwarding' of type Text to type Number.

The sample inputs for the Call Type field are:

conf_in

conf_out

pstn_in

pstn_out

pstn_out_forwarding

pstn_out_transfer

ucap_in

ucap_out_conf

The expected output is just changing the above fields to a nicer text format like in the IF statement

[v-chuncz-msft · Accepted solution]

@Anonymous 

Just replace the minus sign with an equal sign.

'Phone Data'[Call Type] - "pstn_out",