Custom World Bonne on Southern Hemisphere not working

[alphaandromeda]

Example of problem

Custom World Bonne on Southern Hemisphere not working

Used wkt (negative Longitude of natural origin):

PROJCRS["World_Bonne",
    BASEGEOGCRS["WGS 84",
        DATUM["World Geodetic System 1984",
            ELLIPSOID["WGS 84",6378137,298.257223563,
                LENGTHUNIT["metre",1,
                    ID["EPSG",9001]]]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8901]]],
    CONVERSION["World_Bonne",
        METHOD["Bonne",
            ID["EPSG",9827]],
        PARAMETER["Latitude of natural origin",-60,
            ANGLEUNIT["Degree",0.0174532925199433],
            ID["EPSG",8801]],
        PARAMETER["Longitude of natural origin",0,
            ANGLEUNIT["Degree",0.0174532925199433],
            ID["EPSG",8802]],
        PARAMETER["False easting",0,
            LENGTHUNIT["metre",1],
            ID["EPSG",8806]],
        PARAMETER["False northing",0,
            LENGTHUNIT["metre",1],
            ID["EPSG",8807]]],
    CS[Cartesian,2],
        AXIS["(E)",east,
            ORDER[1],
            LENGTHUNIT["metre",1,
                ID["EPSG",9001]]],
        AXIS["(N)",north,
            ORDER[2],
            LENGTHUNIT["metre",1,
                ID["EPSG",9001]]],
    USAGE[
        SCOPE["Not known."],
        AREA["World."],
        BBOX[-90,-180,90,180]]]

C code:

RawByteString srcUtf8 (UTF8Encode (wkt));
srcTmp = proj_create (ProjContext, srcUtf8.c_str());
...
RawByteString tgtUtf8 (UTF8Encode (gcsOfSrc));
tgtTmp = proj_create (ProjContext, tgtUtf8.c_str());
...
const char *const options[] = {"FORCE_OVER=YES", nullptr /* muss mit null terminieren!*/};
ProjTransformer = proj_create_crs_to_crs_from_pj (ProjContext, srcTmp, tgtTmp, nullptr, options);
...
pjPnt = proj_trans (ProjTransformer, PJ_FWD, pjPnt);

Problem description

Transformer from GCS to CRS works as expected: 10°/-40° -> 850976.57/2163022.81.
Transformer from the above CRS to it's GCS (geo) does not work - throws!

Expected Output

850976.57/2163022.81 (CRS) -> 10°/-40° (GCS)

Environment Information

• PROJ version 9.1.1
• Operation System Information

Installation method

• C-Api via DLLs

[mwtoews]

I'm seeing the error:

input string: parsing of user string failed: unhandled parameter value type : **-60**

Is the verbatim WKT in the issue correct? Changing **-60** to -60 should fix the issue.

[alphaandromeda]

It is not that easy - use -60 as value and you get the error.
(I tried to markup it as bold thats why ** is inside wkt).