The simplified invoice (FS) does not allow by law total more than 100 euros (or 1000 for Retail).
If your CAE supports Retail (Confirm please with your accountant), you may use the FS for transactions up to 1000 euros VAT incl.
However, only the Simplified Invoice is subject to these limits. You can use the Invoice / Receipt type that is an equivalent cash-sales bill yet with no amount limit. Note that this series requires the specification of VAT ID number as per the Portuguese VAT directives.
For further information please contact the Gestix technical support service.