AHAH Greta - who has not pressed Alt-F1 for help - https://openvpms.org/documentation/csh/1.9/admin/template/email/edit which says (in part):

Source Expressions

The Source Expressions can be any expression or variable that sets the object to evaluate the content against.  This can be:

• a macro variable , ie $customer, $patient, etc
• a period (.) meaning the current document. This is most useful when creating cover-notes for use when emailing documents via the Print|Email operation.
• left blank. For pre-filled emails, the invoice or document etc will be passed. In this case, it is equivalent to using a period.
• an xpath expression returning an archetype object e.g. openvpms:get(., 'patient.entity')

So yours is failing because $receipt is not one of the available macro variables.
What you want is something like:

where both the Subject and Content sources have been set to a period.

The Subject expression will just produce some like 'Receipt 123456'. You will want to change this to concat($location.name," - ",openvpms:get(.,"displayName")," ",id)

I have attached the General.odt file. Use this as a guide to adjusting yours - or better edit General.odt to customise for your practice so that you have a cover note that will work for other things such a credit notes etc.

Regards, Tim G