code: async function calculateTtl (ttl = 0, relative = true) {
    if (ttl === 0) return 0
    if (ttl < 0) throw new Error('ttl must be greater than 0')
  
    if (relative) {
      const { height } = await this.api.getCurrentKeyBlock()
      return +(height) + ttl
    }
    return ttl
  }
docs: Compute the absolute ttl by adding the ttl to the current height of the chain
  
  @param {number} ttl
  @param {boolean} relative ttl is absolute or relative(default: true(relative))
  @return {number} Absolute Ttl