Some barcodes carry data in a standard format that the scanner at the other end understands: a product code, a batch number, an expiry date. GS1 is the format of logistics and retail; HIBC is the one of the health industry. You choose them with Encoding, in the Barcode section.

Which barcodes support them
GS1	Aztec, Code 128, Code 16K, Code 49, Code One, Data Matrix, Dot Code, QR Code and Ultracode.
HIBC	Aztec, Code 128, Code 39, Data Matrix, PDF 417 and QR Code.

There's no separate GS1-128 or GS1 DataMatrix in the list: GS1-128 - also called EAN-128 - is Code 128 with Encoding set to GS1, and GS1 DataMatrix is Data Matrix with GS1. The element library has them ready-made, in the Barcodes categories.

Writing GS1 data. Put each application identifier in square brackets, followed by its data - no spaces:

[01]09501101530003[17]271231[10]ABC123

That's a product code (01), an expiry date (17) and a batch number (10). Labeljoy adds the separators the standard needs between the parts, and checks the length of each. On the label, the readable line shows the identifiers in round brackets, as the standard prints them: (01)09501101530003(17)271231(10)ABC123.

What goes wrong
Message must start with an Application Identifier.	The data has to begin with an identifier in square brackets.
Invalid data length for Application Identifier	The data after that identifier is too long or too short for it - an expiry date is always 6 digits, for example.
Extended ASCII characters are not supported.	GS1 data takes plain letters, digits and a few symbols only - no accented letters.

HIBC data uses the characters of Code 39 - capital letters, digits and a few symbols - up to 110 of them. Labeljoy adds the leading + if you leave it out, and works out the check character at the end.

When you change the Symbology to one that doesn't support the Encoding you chose, Encoding goes back to Standard.

GS1 composite. For Code 128 in GS1, Databar, EAN and UPC you can add a second, small 2D part above the barcode, for extra data: fill in GS1 composite under the text to encode, and choose GS1 composite mode - CCA, CCB or CCC, from the smallest to the one that holds the most. CCC is for Code 128 only: Databar, EAN and UPC have CCA and CCB.