Ethnomathematics-based learning has been effective for students' mathematical communication skills, but it can still be optimized by minimizing common student errors. Therefore, the objectives of this study are to analyze the shortcomings of students to solve mathematical communication problems in terms of students' skill categories; 2) analyze the learning process based on ethnomathematics with the help of the geoGebra application; 3) Develop learning steps based on ethnomathematics, analysing the shortcomings of the students. The study subjects were courageously selected, i.e. 36 students from the IX semester of the 2023/2024 academic year. Data were obtained through reported math skills, interest questionnaires, observation sheets, and dialogue sheets. Data analysis techniques begin with data analysis, testing students' mathematical communication skills, analyzing qualitative data, interpreting research results, and analyzing quantitative data. According to the analysis of the errors made by the students in solving mathematical communication problems, in terms of the categories of student ability, the students made more procedural errors in the categories of medium and low skills. At the same time, students in the high-ability category tend not to make significant mistakes. The results of the triangulation found two stages of learning necessary to minimize student errors, i.e., the exercise stage and the research stage. The stages of ethnothematic learning are exploration, mapping, explanation, exercise, research, and reflection. The effectiveness of the learning model developed in the mathematical communicative skills of the students will be analyzed for future research.