You did not provide your GeoJSON file, and I am not sure if it is because my own GeoJSON file is incorrect that no vegetation can be generated.

{
"type" : "FeatureCollection",
"name" : "forest",
"features" : [
{
"type" : "Feature",
"properties":{
"name":"group-1",
"type": 1
},
"geometry" : {
"type" : "Polygon",
"coordinates" : [
[
[ -1.852010886, 52.5291051416 ],
[ -1.8516281235, 52.5299201322 ],
[ -1.8532867597, 52.5303082174 ],
[ -1.8532229659, 52.5307739157 ],
[ -1.8546902214, 52.5310455705 ],
[ -1.854690222, 52.529570852 ],
[ -1.8582945656, 52.5302306002 ],
[ -1.8584859472, 52.5290857372 ],
[ -1.8531591732, 52.5280378689 ],
[ -1.8463013496, 52.5282901358 ],
[ -1.8463970413, 52.5290275229 ],
[ -1.8512949189, 52.5290952576 ],
[ -1.852010886, 52.5291051416 ]
]
]
},
"properties" : {
"id" : 22,
"OBJECTID" : 22,
"IndividualOrOrganisation" : "Individual",
"FirstName" : "Example First Name",
"LastName" : "Example Last Name",
"OrganisationName" : "WMCA",
"TreeCount" : 18,
"TreeType" : "Mixed woodland (broadleaf and conifer)",
"PrivacyPolicyAgreement" : "Yes",
"ShowOnMap" : "Yes",
"Reason" : "To provide fruit",
"DatePlanted" : "30/06/2023"
}
}
]
}