Cannot assign void to an implicit type variable

I'm not sure what's happening to my code. I'm following the course and the idea is to create in the form a place to upload image using my C# .Net + Angular gallery manager application. The error happens at var galeria = await _galeriaService.GetGaleriaByIdAsync(galeriaId, true);:

Cannot assign void to an implicit type variable CS0815.

The following map is from my controller:

 [HttpPost("upload-image/{galeriaId}")]
    public async Task<IActionResult> UploadImage(int galeriaId)
    {
        try {
            var galeria = await _galeriaService.GetGaleriaByIdAsync(galeriaId, true);
            if(galeria == null) return NoContent();

            var file = Request.Form.Files[0];
            if (file.Length > 0)
            {
                // DeleteImage(galeria.ImagemURL);
                //galeria.ImagemURL = SaveImage(file);
            }
            var GaleriaRetorno = await _galeriaService.UpdateGaleria(galeriaId, galeria);

            return Ok(GaleriaRetorno);
        }
        catch (Exception ex)
        {
            return this.StatusCode(StatusCodes.Status500InternalServerError, $"Erro ao tentar adicionar galeria. Erro {ex.Message}");
        }
         
    }

Return type of GetGaleriaByIdAsync

Task<Galeria> IGaleriaService.GetGaleriaByIdAsync(int galeriaId)
    {
        throw new NotImplementedException();
    }

IGaleriaService

namespace GestorGaleria.Application.Contratos
{
    public interface IGaleriaService
    {
        Task<GaleriaDto> AddGaleria(GaleriaDto model);

        Task<GaleriaDto> UpdateGaleria(int id, GaleriaDto model);

        Task<bool> DeleteGaleria(int id);

        Task<GaleriaDto[]> GetAllGaleriasAsync();
    
        Task UpdateGaleria(int galeriaId, Galeria galeria);
        
        Task<Galeria> GetGaleriaByIdAsync(int galeriaId);

    }
}