May be you have some complex content in your footnotes.
Try this note.lua file:

function Note(note)
  if #note.content == 1 then
    table.insert(note.content[1].content, 1, pandoc.Str "%%opening%%")
    table.insert(note.content[1].content, pandoc.Str "%%closing%%")
    return note.content[1].content
  end
  return note
end

Le mercredi 19 juillet 2023 à 19:59:23 UTC+2, Christophe Demko a écrit :

> Can you post the files which cause an issue ?
>
> Le mercredi 19 juillet 2023 à 18:44:09 UTC+2, 'o-Dzin Tridral a écrit :
>
>> Hi Christophe,
>>
>> I'm sorry to follow up again, but I get an error with my large md file
>>
>> The filter fails with the error
>>
>>   attempt to concatenate a nil value (field 'text')
>>
>> The error doesn't mention where the failure happens or what text is 
>> causing the problem.  If you have any advice re how to get more information 
>> from pandoc or lua I would very much appreciate it. 
>>
>> I entirely understand if you don't have time to look at this of course.
>>
>> best regards,
>>
>> 'ö-Dzin
>>
>>  
>>
>>
>> འོད་འཛིན་དྲི་བྲལ
>> 'ö-Dzin Tridral
>> [image: https://]about.me/tridral
>>
>> <https://about.me/tridral?promo=email_sig&utm_source=email_sig&utm_medium=email_sig&utm_campaign=external_links>
>> ☸ 
>> *Drala Jong Appeal - creating a Buddhist retreat centre in Wales: 
>> https://www.drala-jong.org/ <https://www.drala-jong.org/> *☸
>>
>> ☸ Achos pan ddaw y Pedwar Marchog i ofyn a roist ti o dy gyfan - fydd 
>> gen ti ddim esgus - Meinir Gwilym ☸
>>
>>
>> On Wed, 19 Jul 2023 at 17:19, 'o-Dzin Tridral <tri...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>>
>>> Hi Christophe,
>>>
>>> Thank you very much for your reply.
>>>
>>> I've not used lua filters before.  It took me a while to realise how to 
>>> make a command line with the input file and output file.
>>>
>>> I thought I'd write back and include tis for the benefit of any novices 
>>> like me.
>>>
>>> I've now done this with your script, inserting the* '-i' *for the input 
>>> file and using output redirection '*>'  *for the output file
>>>
>>>    pandoc --lua-filter note.lua -t markdown -i *<input file>* | sed -e 
>>> 's/%%opening%%/\^\[/g' | sed -e 's/%%closing%%/\]/g' > *<output file>*
>>>
>>> This works on my small example file.
>>>
>>> Thank you once again.
>>>
>>> 'ö-Dzin
>>>
>>>  
>>>
>>>
>>> འོད་འཛིན་དྲི་བྲལ
>>> 'ö-Dzin Tridral
>>> [image: https://]about.me/tridral
>>>
>>> <https://about.me/tridral?promo=email_sig&utm_source=email_sig&utm_medium=email_sig&utm_campaign=external_links>
>>> ☸ 
>>> *Drala Jong Appeal - creating a Buddhist retreat centre in Wales: 
>>> https://www.drala-jong.org/ <https://www.drala-jong.org/> *☸
>>>
>>> ☸ Achos pan ddaw y Pedwar Marchog i ofyn a roist ti o dy gyfan - fydd 
>>> gen ti ddim esgus - Meinir Gwilym ☸
>>>
>>>
>>> On Wed, 19 Jul 2023 at 14:36, Christophe Demko <chd...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>>>
>>>> You can use a lua filter:
>>>>
>>>> $ pandoc --lua-filter note.lua -t markdown | sed -e 
>>>> 's/%%opening%%/\^\[/g' | sed -e 's/%%closing%%/\]/g'
>>>>
>>>> with this note.lua file
>>>>
>>>> function Note(note)
>>>>   note.content[1].content[1].text = "%%opening%%" .. 
>>>> note.content[1].content[1].text
>>>>   note.content[1].content[#note.content[1].content].text = 
>>>> note.content[1].content[#note.content[1].content].text .. "%%closing%%"
>>>>   return note.content[1].content
>>>> end
>>>> Le dimanche 16 juillet 2023 à 17:35:38 UTC+2, tri...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org a 
>>>> écrit :
>>>>
>>>>> Is it possible to use Pandoc to convert an md file that has reference 
>>>>> footnotes to one that has inline footnotes - just by going from md -> md, 
>>>>> but failing that via another format.
>>>>>
>>>>> I have a file containing reference footnotes like this
>>>>> ----
>>>>>     Example[^1] line of text.
>>>>>
>>>>>     [^1]: Example footnote
>>>>> ----
>>>>>
>>>>> I would like to convert them all to inline footnotes like this
>>>>>
>>>>> ----
>>>>>     Example^[Example footnote] line of text.
>>>>> ----
>>>>>
>>>>> Thank you for any help
>>>>>
>>>>> 'ö-Dzin
>>>>>
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>>>> .
>>>>
>>>

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