If you are including the Heading 1 number in the page number field then the maths to add 1 to it doesn't work on the {page} field because it is no longer a simple arabic number. You can make it become an arabic number which can then be added by including a format switch. This will mean you need to include a separate StyleRef field to bring in the Chapter/Heading number and also add the hyphen separator outside of the page number calculation field.

Using the page number as you have currently configured, the footer should be
FP:{Page} / (FP: {StyleRef "Heading 1" \n}-{={Page \* Arabic}+1} Blank)

If you changed the page number setting for the section to NOT include the Chapter number, your fields could be modified to
FP:{StyleRef "Heading 1" \n}-{Page} / (FP: {StyleRef "Heading 1" \n}-{={Page}+1} Blank)

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Andrew Lockton
Chrysalis Design, Melbourne Australia