To generate the API in TypeScript with the attribute name's first letter not capitalized, you can use the --model-name-prefix option in the openapi-generator-cli command. This will allow you to specify a prefix that will be added to the beginning of all generated model names. For example:

openapi-generator-cli generate -i /path/to/spec.yaml -g typescript-fetch -o /output/directory --model-name-prefix=''

This will generate the TypeScript API in the specified output directory, and the attribute names in the generated models will have the first letter not capitalized.