I got there in the end, chat gpt did eventually work for me, after a bit of debugging and error handling.

For anyone in the same boat, hopefully this code can help.

    let
    // Define the Table.GenerateByPage function for pagination
    Table.GenerateByPage = (getNextPage as function) as table =>
    let        
        listOfPages = List.Generate(
            () => getNextPage(0),            // Start with the first page (skip=0)
            (lastPage) => lastPage <> null,  // Stop when null is returned (no more data)
            (lastPage) => getNextPage(Table.RowCount(lastPage)) // Pass the row count as the next skip value
        ),
        // Concatenate the pages together
        tableOfPages = Table.FromList(listOfPages, Splitter.SplitByNothing(), {"Column1"}),
        firstRow = tableOfPages{0}?
    in
        // If no pages are returned, return an empty table
        if (firstRow = null) then
            Table.FromRows({})
        else if (Table.IsEmpty(firstRow[Column1])) then
            firstRow[Column1]
        else
            Value.ReplaceType(
                Table.ExpandTableColumn(tableOfPages, "Column1", Table.ColumnNames(firstRow[Column1])),
                Value.Type(firstRow[Column1])
            ),

    // Define the getNextPage function with enhanced error handling
    getNextPage = (skipCount as number) =>
    let
        // Construct the API URL with pagination logic
        url = "https://finder.bloodsandbeyond.co.uk/myURL?$skip=" & Number.ToText(skipCount),
        headers = [
            #"x-api-token" = "?????????????????????????"
        ],
        source = try Web.Contents(url, [Headers=headers]) otherwise null,
        // Convert the response to text and parse it as JSON
        rawResponse = if source = null then error "No data from API!" else Text.FromBinary(source),
        jsonResponse = try Json.Document(rawResponse) otherwise null,
        // Check if the "value" field exists and is valid
        value = if jsonResponse = null or not Record.HasFields(jsonResponse, "value") then null else jsonResponse[value],
        // If value is null or empty, stop fetching further pages
        nextPage = if value = null or List.IsEmpty(value) then null else value
    in
        // Return the result as a table or null
        if nextPage = null then null else Table.FromList(nextPage, Splitter.SplitByNothing(), null, null, ExtraValues.Error),

    // Use Table.GenerateByPage to get all data
    allData = Table.GenerateByPage(getNextPage)
in
    allData