Walkthrough for creating WWT tiles fails with mProjectQL giving "Invalid projection"

[pandapawskat]

Following these steps
http://montage.ipac.caltech.edu/docs/WWT/
fails at the "Generating tile FITS images" step. mProjectQL gives this output on the very first (level 0, all-sky) tile:
[struct stat="ERROR", msg="Invalid projection"]

I am using the version of Montage that apt installed for me on Ubuntu:
montage/jammy,now 6.0+dfsg-7build5 amd64

Here's the header:

SIMPLE  =                    T
BITPIX  =                  -64
NAXIS   =                    2
NAXIS1  =                  256 / All WWT tiles are 256x256 pixels.
NAXIS2  =                  256
CTYPE1  = 'RA---TOA'
CTYPE2  = 'DEC--TOA'
CRPIX1  =                -0.50
CRPIX2  =                -0.50
PV2_1   =                    0 / HTM level for this tile.
XTILE   =                    0 / X and Y tile indices.  That is, the tile
YTILE   =                    0 / location in the array of tiles at this level.
CDELT1  =                 1.00 / The rest of the header is really just
CDELT2  =                 1.00 / boilerplate.  Don't let the values get
CRVAL1  =                   0. / modified as it might affect proper
CRVAL2  =                   0. / processing.
PC1_1   =                 1.00
PC1_2   =                 0.00
PC2_1   =                 0.00
PC2_2   =                 1.00
END